Electrolytic recovery of metals from solutions



June: 11 9 'WZKESO ELECTROLYTIC RECOVERY OF METALS FROM SOLUTIONS FiledJan. 51,

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Patented June 1, 19236.

UNITED STATES URLYN C. TAINTON, OF JOHANNESBURG, TRANSVAAL, SOUTHAFRICA.

ELECTROLYTIC RECOVERY OF MET ALS FROM SOLUTIONS.

Application filed January 31, 1923. Serial No.- 616,167.

This invention relates to the electrolysis of solutions with. insolubleanodes and is intended especially to prevent the disintegration of theseanodes which is apt to occur during this operation.

The problem of finding an anode which will not disintegrate on continueduse is one which for many electrolytic operations has not yet beensolved. For example,.in the electrolysis of cyanide solutions there isno available commercial material which does not disintegrate underanodic service with greater or less rapidity. The same is true of theelectrolysis of brine solutions for the production of chlorine andespecially in the electrolytic precipitation of metals, such as lead andsilver, which have been dissolved from ores in the acid brine leachingprocess. This anode problem often becomes more acute where it isnecessary to employ diaphragms to separate the electrodes.

if have found that the disintegration of the anode is due to thepresence irr the solution of certain substances (often in minutequantities) which bring dbbut this deleterious efi'ect. If thesesubstances are re moved or kept from contact with the anode, thedisintegration is minimized or eliminated. For instance in theelectrolysis of brine solutions with carbon or graphite anodes, I havefound that the presence of sulphate ions is the principal factor in thedisintegration. Similarly in the electrolysis of cyanide solutions withlead or lead peroxide anodes, it is mainly the presence of chlorideswhich bring about the ,anode disintegration. A lead anode is practicallypermanent in a solution containing only sulphate ions. And in the sameway for each given insoluble anode, a solution can be prepared which hasno disintegrating effect.

lln order to carry my invention into eflect, I make use of a diaphragmwhich separates the electrolytic cell 1nto two compartments, such asillustrated in the accompanying drawings, in which Fig. 1 is adiagrammatic view showing an arrangement of apparatus where it isdesired to make use of a precipitated cathode solution for circulationthrough the anode chamber.

Fig. 2 isa diagrammatic view showing an arrangement of apparatus whereit is not practicable to remove the impurities from a lead solution andwhere a separate solution may be used for the anodes The anode may be ofany suitable material, for instance,

lead, graphite, etc., and it is surrounded by a solution of appropriatecomposition. For example, with a lead anode a solution of sulphuric acidor sodium sulphate, substantially free from chlorides, is employed as.illustrated in Fig. 2. For a raphite anode a solution of a chloride, sustantially free from sulphates, shouldbe used as illustrated in Fig. 1.I

If the solution in the cathode compartment containsacid radicles oranions capable of attacking the anode in question, these anions willtend to drift into the anode rcompartment under the influence ofthe'potential gradient. In order to avoid this condition it is necessaryto feed in fresh solution to the anode chamber either intermittently orcontinuously so that the static head so created inside the anode chamberwill tend to carry back these anions as they tend to drift in throughthe diaphragm. This effect may also be secured by providing two ports,an inlet and an outlet port, to the anode chamber and arranging for afairly rapid feed of the proper solution through the anode chamberwhereby the objectionable anions are carried out before they can attaina concentration suiiiciently high to be detrimental.

As an example of the, practical operation of this invention as appliedto the electrolysis of cyanide solutions, an apparatus. of the generaltype described in my Patent No. 1,231,967,.July 3, 1917, entitledRecovery of metals from solutions and apparatus there for may be used.The cathode is of a porous conducting material and the solution to bepreciptated is passed through this cathode. The anode may be oflead andis separated from the current cyanide solution by a permeable diaphragmof canvas, wood veneer, or similar material. To the anode chamber 'soformed, there are two ports and a steady stream of a solution of puresodium sulphate is arranged to flow in at one port and out at the other.The level 'of the outlet port is preferably so arranged that there is aslightly higher pressure inside the anode chamber than there is in thecathode chamber so that the anolyte tends to drift outwards and preventthe entry of anions (such as chlorides)v which would tend to causedisintegration of the anode,

In the same way in the recovery of lead and silver which have beendissolved in nee brine solutions, an apparatus of the kind described inmy prior Patent No. 1,251,302, December 25, 1917, entitled Electrolyticrecovery of metals from their solutions, may be used. lln this case agraphite anode may be conveniently employed and a solution of a chloride(such as sodium chloride) substantially free from sulphates may beemployed as an anolyte. This solution may be prepared by treating abrine solution with barium or calcium chloride. It is often convenientto make use of the leaching solution itself for this purpose and inorder to do this a small quantity of calcium chloride is added to theleaching solution.

After the lead and silver are taken up from the ore, the solution ispassed through the electrolytic cell and the metals precipitated. Theprecipitated solution, now substantially free from lead and silver, aswell as from sulphates, is fed through the anode compartment as abovedescribed before being returned to the ore. In this way two beneficialresults are attained, for not only is the disintegration of the anodesprevented, but the solution is oxidized and saturated with chlorine--acondition favorable to high metal ertrations in the leaching operation.

l have found further that by employing the above mentioned arrangement,it is possible not only to prevent disintegration of the anode surfacebut actually to build it up and improve it. This is done by using ananode solution, containing a salt of a metal,

which will deposit on, and form a protective layer over, the face of theanode. The best metal for this purpose is manganese, althought lead,cobalt. and antimony, may be employed in special instances.

in carrying out the above process as applied for instance to graphiteanodes, the same mechanical arrangement as described above is employedbut as an anolyte solution, a solution of sodium chloride contain--ing'a small quantity of manganese chloride is used. Under continuedelectrolysis an adherent coat of manganese dioxide is formed on theanode and as this is continually renewed, the surface of the anode iseffectually protected from disintegration.

A. brief descript' of Figs. 1 and 2 in the draw' is herewith submitted.l/Vhere it is desire to malts use of the precipitated catholyte solutionfor circulation through th onolyte chamhers, an arrangement of applayedas shown in Fig. 1. in tionable impurities are this case removed afterpassi .-.rough the cathode chamber.

T he drawi ilustrates the leaching of a lead. ore with a brine solution.The ore is leached with. the brine solution returning from theelectrolithic cells. Before this solution goes on the ore is mixed withto solution either before or,

calcium chloride solution. This calcium chloride precipitates thesulphates which would otherwise cause disintegration of the anode. Thepurified solution is run first through the cathode chamber toprecipitate the lead and then through the anode cham; ber (note that inthis instance the catholyte is at a higher pressure). There it is notpracticable to remove the impurities-from the lead solution, a separatesolution may be used for the anodes as illustrated in the diagrammaticdrawing marked Fig. 2. This drawing illustrates the leaching of a silverore with cyanide solution. In this case the solution, afterprecipitation of the metal in the cathode chamber of the cell, returnsto the leaching tank. The anode department is filled with a dilutesolution of sulphuric acid and a lead anode is employed. The

anolyte solution is kept at a slightly higher I pressure to ofl'set theionic draft through the diaphragm.

Having thus described my invention, what ll claim and desire to secureby Letters Patent is 1. ln the electrolysis with insoluble anodes ofsolutions which tend to cause disintegration of said anodes, a method ofoperation which consists in enclosing the anode with a porous partitionand feeding to the conr pertinent thus formed, concurrently with theprocess of the electrolysis, a solution of hind which will not attackthe anodes.

2. in the electrolysis with insoluble anodes of solutions which tend tocause disintegration of-said anodes, a method of operation whichconsists in enclosing the anode with a porous partition and feeding tothe com partment thus formed, concurrently with the process of theelectrolysis, a solution of a kind which will not attack the anodes, andregulating the feed of the solution to the anode compartment so thatthere is created a pressure higher than that in the cathode compartment,thus causing a flow through the diaphragm from the anode to the cathodecompartment, and preventing harmful substances from entering the anodecornpartment from the cathode compartment. 3. In the electrolysis withinsoluble of solutions which tend to cause disintegra tion of saidanodes, a method of operation which consists in enclosing. the anode aporous partition feeding to the con pertinent that ormed, concurrentlywit the process of a e ole rolysis, a soi hind while i will attach thisano withdrawing said solution from compartment at a suflicien l rapidprevent accumulation of her from the catholyte solution which would tendto disinte rate the anode.

l. lln the electrolysis with insoluble anodes of solutions which tend tocause oisintc 'rzztion of said anodes, method of ope ful anions whichconsists in enclosing the anode with a porous partition and feeding tothe corn partment thus formed, concurrently with the process ofthecelectrolysis, a solution of a kind which will not attack the anodes,and adding to the solution a salt of a metal which will form a depositof an oxide on the anode surface and protect it against corrosion.

In the electrolysis with insoluble anodes of chloride solutions whichcontain substances (anions) of a kind which tend to cause disintegrationof said anodes, a method of operation which consists in separating theanodes from the catholyte by permeable diaphragms to form a cathodecompartment and an anode compartment, maintaining a circulation of acatholyte solution throu h the cathode compartment to precipitate t 1emetals contained, and returning and circulating the catholyte afterprecipitation of the metal through the anode compartment to expelobjectionable anions and to oxidize and saturate the solution withchlorine.

6. In the electrolysis with insoluble anodes of solutions which containsubstances (anions) of a kind which tend to cause disintegration of saidanodes, a method of operation which consists in separating the anodesfrom the catholyte by permeable diaphragms and maintaining a circulationthrough the anode compartment so formed a solution of a kind which willnot attack the anodes.

7. In the electrolysis withinsoluble lead anodes of cyanide solutionswhich contain substances (anions) of a kind which tend to causedisintegration of the said anode, a method of operation which consistsin separating the anodes from the catholyte by permeable diaphragms, andmaintaining a circulation through the. anode compartment so formed of asolution containing a large excess of sulphate ions.

8. In the electrolysis with insoluble anodes of chloride solutions whichcontain substances (anions) of a kind which tend to cause disintegrationof the anodes, a method of treatment which consists in removing from thesolution before it comes in contact with the anodes the anions whichcause disintegration of the anodes.

9. In the electrolysis with insoluble anodes of solutions which tend tocause disintegration of the anodes, a method of operation which consistsin enclosing the anodes with a porous partition and feeding to thecompartment so formed, concurrently with the progress of electrolysis, asolution containmg the salt of a metal which will form a deposit oi anoxide on the anode surface and protect it against corrosion.

URLYN o. TAINTON.

